Capacitors, which have high reliability in rapid charge and discharge, are used in various technical fields. A conventional electric double layer capacitor described in Patent Document 1 out of such capacitors includes positive and negative electrodes polarizable electrode layers mainly made of activated carbon. The electric double layer capacitor with aqueous electrolyte has a withstand voltage of 1.2V. The capacitor with organic electrolyte has a withstand voltage ranging from 2.5 to 3.3V.
Since energy of the capacitor is proportional to the square of its withstand voltage, the capacitor with the organic electrolyte (high withstand voltage) has higher energy than the capacitor with the aqueous electrolyte. Even the electric double layer capacitor with the organic electrolyte, however, has an energy density less than 1/10 of that of a secondary battery, such as a lead-acid battery. Capacitors are required to have larger energy density.
It is known that, to improve the durability of such capacitors, a separator made of resin, such as polyethylene and polypropylene, is used.
A conventional capacitor includes a separator having a sheet shape for isolation between the positive and negative electrodes. In view of manufacturing and strength, the separator necessarily has a thickness of approximately 25 μm, thus being prevented from having a small thickness and a large capacitance.    Patent Document 1: JP10-270293A